The present invention relates to a process for the preparation of the surface of a uranium and titanium alloy member, more particularly containing 0.6 to 0.8% by weight titanium, said process being performed with a view to carrying out nickel coating or plating of said member by a chemical nickel plating process.
It is more particularly used in the medical field (protective shield in radiology), the maritime field (ballast or armour plating) and the space field (satellites).
In numerous fields, it is frequently necessary to deposit nickel coatings on uranium and titanium alloy members. These coatings are generally produced by electrolytic nickel plating making it possible to generally obtain coatings with an adequate quality. However, these electrolytic nickel plating processes are not suitable for the treatment of members having a complicated shape with angles and/or holes, because in such cases it is difficult to obtain a nickel deposit of uniform thickness and sometimes even to completely coat the surface of the members. Moreover, in the case of members having a complex shape, it is preferable to deposit the nickel chemically in order to surmount these difficulties.
In the case of a nickel coating produced by chemical nickel plating, in order to obtain a coating having an adequate adhesion, it is necessary to subject the member to a prior surface preparation treatment, which can be carried out by chemical etching. The latter must be uniform and thickness-controllable, so that the prepared member surface is able to receive the nickel deposit.
The presently known surface treatment processes for uranium and titanium alloy members do not make it possible to obtain a thickness-uniform, homogeneous etching over the entire surface of the member to be treated, when the latter has a complex shape.
Moreover, when interest is attached to the reprocessing of solutions containing uranium, the presently used etching solutions for the surface treatment of uranium and titanium alloy members permit little or no recovery of the uranium dissolved during chemical etching. This uranium recovery makes it possible to limit the production of waste and therefore partly obviate the problems connected with the storage of waste.
FR-A No. 1564575 discloses a process for the preparation of a surface of a uranium or uranium alloy member with a view to carrying out electrolytic nickel plating. This process in particular involves an anodic pickling stage carried out in a solution containing a magnesium and/or lithium salt.
This anodic pickling stage is suitable for an electrolytic nickel deposition, but is inappropriate for chemical nickel deposition. In particular, tensile strength tests on the members having undergone said anodic pickling, followed by chemical nickel plating lead to the separation of the nickel coating, which is contrary to the sought objective.
Moreover, the lithium and/or magnesium salts used in the aforementioned patent specification do not permit the recovery of the uranium dissolved in the electrolytic solution, as a result of the complexing of the uranium with the anion of said salts and/or rapidly poison the system for the extraction of the dissolved uranium, so that said system rapidly becomes unusable, which is particularly the case with SO.sub.4.sup.- ions.